The numbers for San Mateo County are striking — jobs are booming, but housing growth has stalled and commuters are spending more and more time stuck in traffic.

A new report by housing and transit advocates finds the rejection of new housing developments in the county has led to more, not less, congestion as workers move farther away to find affordable housing. One new home was built in San Mateo County for every 19 jobs created between 2010 and 2015.

Many cities and their residents have fought new development because they are “really concerned about traffic,” said Evelyn Stivers, executive director of the Housing Leadership Council of San Mateo. But, she added, “not building housing really causes traffic problems.”

The report by TransForm, a nonprofit supporting transit and smart growth, and the Housing Leadership Council shows the difficulties expanding transit and housing in a county that hosts the headquarters of Facebook, Oracle, Genentech and other tech giants, and encompasses some of the wealthiest communities in the United States. The median sales price for a home in San Mateo County in April was $1.6 million. The area’s median annual income is $118,400 — less than one-third of the annual salary needed to purchase a home with a 10 percent down payment.

The report comes as county leaders consider a proposal to add a half-cent to the sales tax to raise transportation funds. The plan, which must be approved by the county transit board and elected leaders, would go to voters in November. Planners estimate it would raise $80 million annually.

Several cities in the affluent county has fallen behind state goals for building new housing. As a whole, San Mateo County met about half of its Regional Housing Need Allocation target between 2007 and 2014. Menlo Park built 29 percent of its goal, San Mateo, 39 percent, and Burlingame, 16 percent. Redwood City exceeded its target by issuing permits for nearly 2,500 high-end homes.

Stivers said the the housing shortage threatens to cripple local businesses. Small, downtown shops and restaurants struggle to keep workers, and some have purchased apartment buildings to house their employees, Stivers said. “We’re just falling so short,” she said. “There’s an opportunity to do something better.”

The congestion has made commutes 80 percent longer since 2010, robbing workers of nearly a full work week of time stuck in traffic, according to a 2017 study by the Metropolitan Transportation Commission.

Although the county is home to a growing number of well-paid jobs in tech, those workers are supported by many more low-paid service workers, according to the report. The county has more than 100,000 service and retail workers making less than $25,000 annually.

State planners estimate the county will add more than 30,000 jobs through 2024 for workers earning less than $30,000 annually. Housing for those workers will be hard to find, according to the report.

“The majority are not making enough to live in not just San Mateo, but in the neighboring county,” said Stuart Cohen, executive director of TransForm. The housing shortage has forced many teachers, emergency workers and service employees out of the county, he said.

Even if the county approves higher taxes for transportation improvements, the list of projects is long and expensive. For example, the San Mateo Transportation Authority has used about $110 million in sales tax revenues to upgrade sections of U.S. 101 and the South San Francisco CalTrain station. Funds have also been earmarked for pedestrian and bike lanes.

The report was funded by the Chan-Zuckerberg Initiative, the Hewlett Foundation and several regional community foundations.

Louis Hansen covers housing issues for the Bay Area News Group and is based at The Mercury News. He's won national awards for his investigations and feature stories. Prior to joining the organization, he was an investigative reporter at The Virginian-Pilot, where he covered state government, the military and criminal justice.